1. Field of the Invention
This invention relates to apparatus used in connection with the drilling and servicing of boreholes in the earth, more particularly those frequently referred to as “wells,” such as oil and gas wells. More particularly, this invention relates to apparatus used in connection with the handling and manipulation of tubular strings, commonly referred to as drillstrings and workstrings.
2. Related Art
The drilling of earthen boreholes, namely “wells” (that term being used broadly, to include oil wells, gas wells, saltwater disposal wells, and any other type of earthen borehole), frequently involves the use of a long tubular string, often called a drillstring, which holds a drill bit at its lower end. The drill bit is rotated, either by rotation of the drillstring from the surface via a rotary table or a top drive; or by a downhole device, such as a so-called “mud motor” or turbine.
Certain operations associated with the drilling function result in the drill string being rotationally fixed, yet it is desirable to monitor the torque being imposed on the drillstring. By way of example, from time to time, the drillstring will become stuck in the well (unable to be pulled out of the wellbore, unable to be rotated, etc.), due to one or more of a variety of downhole conditions (sloughing formations, pressure differential sticking, etc.).
Once the drillstring is stuck, various means known in the relevant art must be employed to remove the drillstring, so that the borehole can be re-drilled as necessary. A common sequence is to determine the approximate depth (below the surface or other datum) at which the drillstring is stuck (which is typically done by means of a “free point” tool), then backoff or unscrew the nearest threaded connection above the stuck point. The free section of drillstring can then be retrieved from the wellbore. Efforts can then commence to retrieve the stuck section remaining in the wellbore, frequently involving “washing over” the stuck pipe, engaging the uppermost end of the stuck pipe with a grapple, then commencing efforts to pull the stuck section out of the borehole.
It can be appreciated that in order to back off or unscrew the appropriate threaded connection, reverse torque must be placed on the connection. This task is complicated by the fact that the connection in question may be located many thousands of feet below the rig floor, by way of example 5,000′ to 10,000′ deep. Suffice to say that with such depths, there is considerable yielding of the drillstring over such a long length, and imposing torque at the rig floor by rotating the drillstring in a reverse direction (reverse typically being counter-clockwise, when viewed from above) does not instantly result in torque being applied at the desired connection. In effect, the reverse torque is resisted by friction between the drillstring and the casing/borehole, and/or is effectively absorbed by the rotational elasticity of the drillstring. In order to “work down” torque to the desired connection, the appropriate torque (in terms of number of turns of the drillstring) must be imposed at the surface, then the drillstring is raised and lowered at the surface while the reverse torque is held in place on the drillstring at the surface. The raising and lowering of the drillstring at the surface is due at least in part to stretching of the drillstring. By this means, the reverse torque is gradually worked down to the connection in question. Once the reverse torque is imposed on the desired connection, means known in the art field in question (frequently, an explosive charge lowered on an electric line, called a “string shot”) are employed to impart a localized percussion force at or near the connection, with the goal being that the desired connection (rather than one at a shallower depth) is “backed off” or unscrewed.
It can be seen from the foregoing description that a fundamental part of the backing-off procedure is the imposition of torque (particularly, reverse torque) on the drillstring at the surface (that is, in the working area above the rig floor), and holding the reverse torque on the drillstring while the drillstring is raised and lowered. A device known as a “drillstring swivel,” referred to herein by that term or simply as “swivel,” permits rotating the drillstring below the swivel, while permitting structural elements above the swivel to remain stationary.
A key problem, then, that the present invention addresses is the imposition of torque on the drillstring while raising and lowering the drillstring, in a safe manner. A further problem is that of monitoring the value of the torque on the drillstring during this operation.
One prior art manner of holding torque on the drillstring while raising and lowering same was to use a set of conventional drillpipe tongs hold torque, after the rotary or other means had been used to rotate the drillstring in reverse. A load cell could be placed in the tong holdback line, in order to monitor the force (and consequently torque) being imposed on the drillstring. While the drillstring could then be raised and lowered within the bounds of the length of the tong cable, it can be appreciated that this method carries a number of disadvantages, including:                Limited distance that the drillstring can be raised—constrained by the length of the holdback line on the tongs        Risk of injury to personnel, as this method creates a situation in which mechanical members with very high forces imposed on them are being moved about above the rig floor at heights which could result in serious injury or death if failure occurred. In particular, a line and tong with very high forces thereon are being moved up and down above the rig floor. Should the tong line break, the line could swing around, and/or the tong itself swing around, and strike someone with great force. Similar events could occur should the tongs lose their “bite” on the pipe, or slip, in which case the tong body could swing around with great force.        
Other disadvantages exist to this old method, but the safety aspect is one of the most important.
Other tools were developed in an effort to address the tong and cable issue noted above, said tools are generally referred to as “locking swivels.” Examples of such apparatus known to applicant include those disclosed in U.S. Pat. Nos. 5,996,712 and 6,244,345. These prior art tools comprise internal mechanisms to lock together the two halves of the swivel, making it non-swiveling, or when desired to unlock the swivel and permit the two halves to rotate with respect to one another. These locking swivels permit the top drive unit, rather than the tong/cable, to hold or maintain the desired reverse torque, thereby resolving at least some of the safety issues associated with the tong/cable procedure described above. However, a disadvantage with known locking swivels is that when locked, and consequently some level of torque held in place on the drillstring, the amount of torque on the drillstring cannot be measured or monitored.
There are other operational situations in which it is desired to hold the drillstring against rotation at the surface, while monitoring the torque thereon; an example is directional drilling using downhole motors, where the reactive torque must be held at the surface, while desirably measuring the value of the torque.
The present invention addresses these issues. Namely, the problem of releasably locking the two sides or halves of a swivel to one another, in a rotational sense, by external means, while retaining the ability to monitor torque between the two sides of the swivel, is solved by an apparatus having first and second members, one of said members attached to the exterior of each side of the swivel (that is, one member on one side of the swivel joint, and the other member on the other side of the swivel joint), at least one of said members releasably gripping one side of the swivel, and a means for monitoring and measuring forces between the first and second members, in order to enable torque calculations and the display and monitoring of torque values.